Isocyanate is a very versatile reactive group to yield a variety of linkages (see Scheme I), which have been widely utilized in organic preparations and polymer synthesis.
Linear ployurethane is readily prepared by reacting diisocyanate and diol and polyurea would be resulted if diisocyanate reacts with diamine instead. On the other hand, when isocyanate reacts with epoxide (Scheme II), it yields an oxazolidone derivative. Oxazolidone is a five-member heterocyclic urethane, which should impart chain rigidity and excellent thermal properties to the corresponding polymers. Polymers bearing oxazolidone in both main-chain and side-chain may be synthesized in different approaches; the most convenient method is the process from isocyanate and epoxide. This process of forming oxazolidone-containing polymers depends on several factors, such as catalysts, temperature, and the type and ratio of the reactants.
It is known to prepare poly-2-oxzalidones from diepoxides and diisocyanates by using different catalysts, which include halides of the alkali and alkaline earth metals and the metals of third group of the periodic system, such as LiCl, MgCl2, FeCl3, AlCl3, ZnCl2, quarternary ammonium salts, such as (CH3)4NI and (C2H5)4NBr, complexes of the Lewis acid-Lewis base type, such as LiCl-HMPA, MgCl-HMPA, AlCl3-tris(2-ethylhexyl)phosphine oxide, alcoholates of the alkali metals, alkaline earth metals, such as LiOBu, NaOBu, Mg(OPh)2, Al(OPh)3, and metal-organic compounds of the type ZnR2, Zn(OCOR)2, AlR3 were also used in the past.